The push to toughen state exams for Illinois grade school students triggered widespread drops in 2013 scores, with hundreds of schools in some of the state's poorest communities seeing performances plunge, test results show.

But some schools in affluent suburbs—from Winnetka and Lake Forest to Hinsdale—saw far less severe declines. Even after the state made it harder to pass reading and math exams for third- through eighth-graders, those schools still posted some impressive results, a Tribune analysis found.